Similar to the increasing packaging density in the field of conventional semiconductor devices, which started from single elementary devices, as e.g. diodes and transistors, and has now reached a point where thousands of very small components are three-dimensionally integrated on one chip, the integration of optoelectronic components becomes more and more important. The trend in optoelectronics is towards integration of active optoelectronic devices, passive optical waveguide devices, and functional optical waveguide devices to form complete optoelectronic units such as for example optical heads for optical disks, optical multi/demultiplexers, and circuits for optical computers. Through the optoelectronic integration, a more compact, stable, and functional optical system can be achieved.
OptoElectronic Integrated Circuits (OEICs), also known as Optical Integrated Circuits (OICs), are divided into two main types from the standpoint of materials. When all components of the circuit are integrated on a single substrate, such as Si, GaAs or InP, the type of integration is called monolithic optoelectronic integrated circuit. A typical monolithic optoelectronic integrated circuit with GaAs laser diode 7 and photodiode 8, integrated on a GaAs substrate 5 with planar waveguide 6, is shown in FIG. 1 a). Typical monolithically integrated lasers and other components are described in the article "Integrated Optics Approach for Advanced Semiconductor Lasers", of Y. Suematsu et al., Proceedings of the IEEE, Vol. 75, No. 11, November 1987, pp. 1472-1487. Other examples for the monolithic integration of GaAs components on a Si substrate are given in the U.S. Pat. Nos. 4,890,895, and 4,774,205.
When the components are made of different materials and then bonded together, this is called a hybrid optoelectronic integrated circuit. For example, in a hybrid optical IC, as illustrated in FIG. 1 b), laser diode 3 is made of aluminum gallium arsenide (AlGaAs), the detector-diode 4 of silicon (Si), and the planar waveguide 2, grown on substrate 1, of lithium niobate (LiNbO.sub.3).
Although the monolithic-type OEIC is ideal as an OEIC, implementation is very difficult at present. While the performance of monolithically integrated GaAs components on Si substrates, see U.S. Pat. No. 4,890,895, is good, these components have not yet reached the quality of those fabricated using GaAs substrates. Since typical OEICs consist of a number of different optical components no one substrate material will be optimum for all of them. Thus, a compromise must be made.
The hybrid type, on the other hand, is relatively easy to fabricate, but there is a problem with assembling the basic components. Packaging and alignment of these components is time consuming and expensive. Nevertheless, the hybrid optoelectronic ICs have the great advantage in that what are currently the most appropriate materials and processing techniques for each device can be utilized. Because of these advantages, hybrid integrated optoelectronic circuits will be subject of intensive research and development.
Different hybrid optoelectronic packages are known in the art, where one or more optical fiber(s) is/are connected to an optoelectronic component or waveguide. A silicon chip coupling concept is reported on in the article "Permanent Attachment of Single-Mode Fiber Arrays to Waveguides", of E. J. Murphy et al., IEEE Journal of Lightwave Technology, Vol. LT-3, No. 4, August 1985, pp. 795-798. The coupling concept, described by E. J. Murphy, is based on a silicon chip having V-grooves for mounting a bundle of parallel single-mode fibers. The polished end facets of these fibers are butt-coupled to a substrate with waveguides, using optical cement. H. Kaufmann et al. describe in their article "Self-Adjusted Permanent Attachment of Fibers to GaAs Waveguide Components", published June 1986 in Electronics Letters, Vol. 22, No. 12, pp. 642-644, an alignment scheme for aligning optical fibers to a GaAs chip. This alignment scheme, called V-groove flip-chip mounting technique, is characterized in that two fibers and the GaAs chip are mounted on a substrate with V-groove, the alignment being achieved by moving the fibers towards the chip along this V-groove.
Another principle for the alignment of waveguides and/or fibers to optoelectronic components is reported on in the U.S. Pat. No. 4,892,374. As therein described, an optoelectronic component, e.g. a light emitting diode (LED), is bonded in a recessed part of a substrate such that its light emitting facet is coupled to a waveguide being integrated on this substrate. In the article "Multi-Waveguide/Laser Coupling", of E. B. Flint et al., IBM Technical Disclosure Bulletin, Vol. 31, No. 10, March 1989, pp. 384-386, a hybrid package is disclosed comprising fibers carried by a silicon alignment fixture. For lateral and axial alignments, grooves are formed in the top surface of the laser array which has to be coupled to the array of fibers, and in the alignment fixture. This package allows self-alignment of an array of lasers to an array of fibers. Another passive alignment scheme is described in the publication "Passive Coupling of InGaAsP/InP Laser Array and Singlemode Fibers using Silicon Waferboard", of C. A. Armiento et al., Electronics Letters, Vol. 27, No. 12, June 1991, pp. 1109-1111. A laser array is aligned to an array of fibers by providing for an integration platform with alignment pedestals and standoffs on a substrate with V-grooves in which the fibers are situated.
Some disadvantages of the different hybrid alignment schemes cited above are their cost and time intensive manufacturing and the non-efficient coupling. Another disadvantage is the difficult handling of the small components like lasers and other diodes which have to be precisely bonded to the substrate. The alignment problems are not known in the area of monolithically integrated circuits because the active-, passive-, and functional waveguide-devices are automatically aligned by using special photolithographic masks, with the drawback on the other hand, that all different components have to be made out of the same material.
These known approaches do not allow for an efficient integration of multiple components, waveguides and fibers. No prior art is known, relating to simultaneous and self-adjusting alignment schemes for hybrid integration of multiple active optoelectronic devices, functional optical waveguide devices, and passive optical waveguide devices.